1. Field of the Invention
This invention relates to a biocompatible carrier containing L-arginine and L-arginine oligomers for introduction to a certain target cell population in a vascular region, such as smooth muscle cells or inflammatory cells, requiring modulation to ameliorate a diseased state, particularly for the treatment of stenosis or restenosis following a vascular trauma or disease. Moreover, the invention is directed to a composition containing L-arginine, or L-arginine oligomer thereof combined with a coating on an implantable device.
2. General Background and State of the Art
Percutaneous transluminal coronary angioplasty (PTCA) is a procedure for treating heart disease. A catheter assembly having a balloon portion is introduced percutaneously into the cardiovascular system of a patient via the brachial or femoral artery. The catheter assembly is advanced through the coronary vasculature until the balloon portion is positioned across the occlusive lesion. Once in position across the lesion, the balloon is inflated to a predetermined size to radially compress against the atherosclerotic plaque of the lesion to remodel the lumen wall. The balloon is then deflated to a smaller profile to allow the catheter to be withdrawn from the patient's vasculature.
A problem associated with the above procedure includes formation of intimal flaps or torn arterial linings which can collapse and occlude the conduit after the balloon is deflated. Moreover, thrombosis and restenosis of the artery may develop over several months after the procedure, which may require another angioplasty procedure or a surgical by-pass operation. To reduce the partial or total occlusion of the artery by the collapse of arterial lining and to reduce the chance of the development of thrombosis and restenosis, a stent is implanted in the lumen to maintain the vascular patency.
Stents are used not only as a mechanical intervention but also as a vehicle for providing biological therapy. As a mechanical intervention, stents act as scaffoldings, functioning to physically hold open and, if desired, to expand the wall of the passageway. Typically, stents are capable of being compressed, so that they can be inserted through small vessels via catheters, and then expanded to a larger diameter once they are at the desired location. Examples in patent literature disclosing stents which have been successfully applied in PTCA procedures include stents illustrated in U.S. Pat. No. 4,733,665 issued to Palmaz, U.S. Pat. No. 4,800,882 issued to Gianturco, and U.S. Pat. No. 4,886,062 issued to Wiktor.
Biological therapy can be achieved by medicating the stents. Medicated stents provide for the local administration of a therapeutic substance at the diseased site. In order to provide an efficacious concentration to the treated site, systemic administration of such medication often produces adverse or toxic side effects for the patient. Local delivery is a preferred method of treatment in that smaller total levels of medication are administered in comparison to systemic dosages, but are concentrated at a specific site. Local delivery thus produces fewer side effects and achieves more favorable results. One proposed method for medicating stents involves the use of a polymeric carrier coated onto the surface of a stent. A solution which includes a solvent, a polymer dissolved in the solvent, and a therapeutic substance dispersed in the blend is applied to the stent. The solvent is allowed to evaporate, leaving on the stent surface a coating of the polymer and the therapeutic substance impregnated in the polymer.
Local administration of therapeutic agents via stents has shown some favorable results in reducing restenosis. However, development of restenosis remains a persistent problem which has not been significantly alleviated by therapeutic substances which are currently used in the market. Accordingly, there is a great need for better and more effective therapeutic compositions, and methods of administering the compositions, for the effective treatment of restenosis.
Nitric oxide (NO) has many beneficial effects, including vasodilation and inhibiting smooth muscle cell hyperproliferation. However, the temporal, optical and hydrolytic instability of nitric oxide donor moieties has rendered them inefficient for use in reducing restenosis. For example, it is conventionally known that NO is a free radical, has a very short half life and is fast quenching. As a result, long term benefits of reducing restenosis would be difficult to achieve with the use of conventional NO donors.
L-arginine is an amino acid that can be loaded to a higher total effective dose of NO than a conventional NO donor. One of the advantages of using L-arginine as an NO donor is that the rate of NO release from L-arginine is controlled and sustained, which is an improvement over using conventional NO donors. In addition, several molecular components are required in the biosynthesis of nitric oxide from L-arginine including the enzymes iNOS and eNOS, with L-arginine often being the limiting reagent in this reaction scheme. When L-arginine is absorbed by a cell in the presence of eNOS, nitric oxide is produced. In view of the beneficial effects of NO in reducing restenosis, there is a need in the art for a sustained delivery of L-arginine or L-arginine oligomer released from a stent.